The cAMP/Protein Kinase A Pathway and Virulence in Cryptococcus neoformans

Kronstad, James W.,Hu, Guang-Gan,Choi, Jae-Hyuk The Korean Society of Mycology 2011 Mycobiology Vol.39 No.3

The basidiomycete fungus Cryptococcus neoformans is an important pathogen of immunocompromised people. The ability of the fungus to sense its environment is critical for proliferation and the generation of infectious propagules, as well as for adaptation to the mammalian host during infection. The conserved cAMP/protein kinase A pathway makes an important contribution to sensing, as demonstrated by the phenotypes of mutants with pathway defects. These phenotypes include loss of the ability to mate and to elaborate the key virulence factors capsule and melanin. This review summarizes recent work that reveals new targets of the pathway, new phenotypic consequences of signaling defects, and a more detailed understanding of connections with other aspects of cryptococcal biology including iron regulation, pH sensing, and stress.

Expanding fungal pathogenesis: Cryptococcus breaks out of the opportunistic box

Kronstad, James W.,Attarian, Rodgoun,Cadieux, Brigitte,Choi, Jaehyuk,D'Souza, Cletus A.,Griffiths, Emma J.,Geddes, Jennifer M. H.,Hu, Guanggan,Jung, Won Hee,Kretschmer, Matthias,Saikia, Sanjay,Wang, J Nature Publishing Group, a division of Macmillan P 2011 Nature reviews. Microbiology Vol.9 No.3

Cryptococcus neoformans is generally considered to be an opportunistic fungal pathogen because of its tendency to infect immunocompromised individuals, particularly those infected with HIV. However, this view has been challenged by the recent discovery of specialized interactions between the fungus and its mammalian hosts, and by the emergence of the related species Cryptococcus gattii as a primary pathogen of immunocompetent populations. In this Review, we highlight features of cryptococcal pathogens that reveal their adaptation to the mammalian environment. These features include not only remarkably sophisticated interactions with phagocytic cells to promote intracellular survival, dissemination to the central nervous system and escape, but also surprising morphological and genomic adaptations such as the formation of polyploid giant cells in the lung.

Mini-Review : The cAMP/Protein Kinase A Pathway and Virulence in Cryptococcus neoformans

( James W. Kronstad ),( Guang Gan Hu ),( Jae Hyuk Choi ) 한국균학회 2011 韓國菌學會誌 Vol.39 No.3

The basidiomycete fungus Cryptococcus neoformans is an important pathogen of immunocompromised people. The ability of the fungus to sense its environment is critical for proliferation and the generation of infectious propagules, as well as for adaptation to the mammalian host during infection. The conserved cAMP/protein kinase A pathway makes an important contribution to sensing, as demonstrated by the phenotypes of mutants with pathway defects. These phenotypes include loss of the ability to mate and to elaborate the key virulence factors capsule and melanin. This review summarizes recent work that reveals new targets of the pathway, new phenotypic consequences of signaling defects, and a more detailed understanding of connections with other aspects of cryptococcal biology including iron regulation, pH sensing, and stress.

The iron-responsive, GATA-type transcription factor cir1 influences mating in Cryptococcus neoformans

Jung, Won Hee,Kronstad, James W. Springer-Verlag 2011 Molecules and cells Vol.31 No.1

Iron influences the abundance of the iron regulatory protein Cir1 in the fungal pathogen <i>Cryptococcus neoformans</i>

Jung, Won Hee,Kronstad, James W. Elsevier 2011 FEBS letters Vol.585 No.20

<P><B>Highlights</B></P><P>► The fungus <I>Cryptococcus neoformans</I> is an important pathogen of AIDS patients. ► The transcription factor Cir1 regulates iron uptake and virulence in <I>C. neoformans</I>. ► We examined the influence of iron levels on the abundance of Cir1. ► Iron deprivation results in reduced abundance of Cir1. ► Cir1 stability is also regulated by redox conditions and proteasome activity.</P> <P><B>Abstract</B></P><P>The GATA-type, zinc-finger protein Cir1 regulates iron uptake, iron homeostasis and virulence factor expression in the fungal pathogen <I>Cryptococcus neoformans</I>. The mechanisms by which Cir1 senses iron availability, although as yet undefined, are important for understanding the proliferation of the fungus in mammalian hosts. We investigated the influence of iron availability on Cir1 and found that the abundance of the protein decreases upon iron deprivation. This destabilization was influenced by reducing conditions and by inhibition of proteasome function. The combined data suggest a post-translational mechanism for the control of Cir1 abundance in response to iron and redox status.</P>

The Iron-Responsive, GATA-Type Transcription Factor Cir1 Influences Mating in Cryptococcus neoformans

정원희,James W. Kronstad 한국분자세포생물학회 2011 Molecules and cells Vol.31 No.1

Mating and sexual development have been associated with virulence in various fungal pathogens including Cryptococcus neoformans. This fungus is a significant pathogen of humans because it causes life-threatening cryptococcal meningitis in immunocompromised people such as AIDS patients. The virulence of C. neoformans is known to be associated with the mating type of the cells(α or a), with the  mating type being predominant among clinical isolates. However, the mechanisms by which mating and sexual development are controlled by environmental conditions and their relationship with virulence require further investigation. Cir1 is a GATA-type transcription factor that regulates the expression of genes required for utilization of essential metals such as iron and copper, and also genes required for major virulence factors including the polysaccharide capsule and melanin. Here we investigated the role of Cir1 in the mating of C. neoformans. Our results demonstrate that mutants lacking CIR1 are defective in mating, and that Cir1 contributes to copper mediated enhancement of sexual filamentation. Furthermore, we found that Cir1 influences the expression of mating pheromone genes suggesting that this protein plays a role in the early phase of sexual development on V8 mating medium.

The cAMP/protein kinase A signaling pathway in pathogenic basidiomycete fungi: Connections with iron homeostasis

최재혁,정원희,James W. Kronstad 한국미생물학회 2015 The journal of microbiology Vol.53 No.9

A number of pathogenic species of basidiomycete fungi are either life-threatening pathogens of humans or major economic pests for crop production. Sensing the host is a key aspect of pathogen proliferation during disease, and signal transduction pathways are critically important for detecting environmental conditions and facilitating adaptation. This review focuses on the contributions of the cAMP/protein kinase A (PKA) signaling pathway in Cryptococcus neoformans, a species that causes meningitis in humans, and Ustilago maydis, a model phytopathogen that causes a smut disease on maize. Environmental sensing by the cAMP/PKA pathway regulates the production of key virulence traits in C. neoformans including the polysaccharide capsule and melanin. For U. maydis, the pathway controls the dimorphic transition from budding growth to the filamentous cell type required for proliferation in plant tissue. We discuss recent advances in identifying new components of the cAMP/PKA pathway in these pathogens and highlight an emerging theme that pathway signaling influences iron acquisition.

밀 登熟期間의 種實 硬度와 蛋白質含量 變化

Byung Han Choi(崔炳漢),Warren E. Kronstad 한국육종학회 1992 한국육종학회지 Vol.24 No.2

Wheat grain is consumed after a some type of milling followed by cooking. The type and quality of products obtained from wheat grains depend on the type and quality of the grain used and its processing. The major objective of the study was to investigate the changes of grain hardness and protein content during the grain-filling period of ten winter wheat cultivars. Significant differences among the cultivars were observed for time, duration and rate of heading, flowering, grain filling and physiological maturity, and for grain yield and yield components. Yamhill, JD/JB/GB and Shi 3311 belonged to soft grain wheat cultivars, Bolal, Centurk, Shi 4468, and Peking 15 belonged to hard grain wheat cultivars, and with intermediate-hard grains of Hyslop, Kavkaz and Peking 8. In general, grain hardness increased from early grain-filling stage to physiological maturity, while grain protein content decreased from maximum content at early grain-filling stage to minimum content at physiological maturity. Yamhill, Bolal, Centurk, Shi 3311, Peking 15 maintained nearly constant content of grain protein from physiological maturity to harvesting time. However, Hyslop, JD/JB/GB, Kavkaz, Shi 4468 presented decreasing trend of grain protein content after physiological maturity until harvesting time. Thus, the most desirable cultivars were Yamhill with soft grains and Centurk with hard grains because of their stabilized constant content of grain protein after physiological maturity.

The ZIP family zinc transporters support the virulence of Cryptococcus neoformans

Do, E.,Hu, G.,Caza, M. l.,Kronstad, J. W.,Jung, W. H. Informa Healthcare 2016 Medical mycology Vol.54 No.6

<P>Zinc is an essential element in living organisms and a cofactor for various metalloproteins. To disseminate and survive, a pathogenic microbe must obtain zinc from the host, which is an environment with extremely limited zinc availability. In this study, we investigated the roles of the ZIP family zinc transporters Zip1 and Zip2 in the human pathogenic fungus Cryptococcus neoformans. Zip1 and Zip2 are homologous to Zrt1 and Zrt2 of the model fungus, Saccharomyces cerevisiae, respectively. We found that the expression of ZIP1 was regulated by the zinc concentration in the environment. Furthermore, the mutant lacking ZIP1 displayed a severe growth defect under zinc-limited conditions, while the mutant lacking ZIP2 displayed normal growth. Inductively coupled plasma-atomic emission spectroscopy analysis showed that the absence of Zip1 expression significantly reduced total cellular zinc levels relative to that in the wild type, while overexpression of Zip1 was associated with increased cellular zinc levels. These findings suggested that Zip1 plays roles in zinc uptake in C. neoformans. We also constructed a Zip1-FLAG fusion protein and found, by immunofluorescence, not only that the protein was localized to the periphery implying it is a membrane transporter, but also that the protein was N-glycosylated. Furthermore, the mutant lacking ZIP1 showed attenuated virulence in a murine inhalation model of cryptococcosis and reduced survival within murine macrophages. Overall, our data suggest that Zip1 plays essential roles in zinc transport and the virulence of C. neoformans.</P>

Role of Ferroxidases in Iron Uptake and Virulence of Cryptococcus neoformans

Jung, Won Hee,Hu, Guanggan,Kuo, Wayne,Kronstad, James W. American Society for Microbiology 2009 EUKARYOTIC CELL Vol.8 No.10

<B>ABSTRACT</B><P>Iron acquisition is a critical aspect of the virulence of many pathogenic microbes, and iron limitation is an important defense mechanism for mammalian hosts. We are examining mechanisms of iron regulation and acquisition in the fungal pathogen <I>Cryptococcus neoformans</I>, and here, we characterize the roles of the ferroxidases Cfo1 and Cfo2. Cfo1 is required for the reductive iron uptake system that mediates the utilization of transferrin, an important iron source for <I>C. neoformans</I> during infection. The virulence of a <I>cfo1</I> mutant was attenuated in a mouse model of cryptococcosis, and the mutant also displayed increased sensitivities to the antifungal drugs fluconazole and amphotericin B. Wild-type levels of drug sensitivity were restored by the addition of exogenous heme, which suggested that reduced levels of intracellular iron may curtail heme levels and interfere with ergosterol biosynthesis. We constructed green fluorescent protein (GFP) fusion proteins and found elevated expression of Cfo1-GFP upon iron limitation, as well as localization of the fusion to the plasma membrane. Trafficking to this location was disrupted by a defect in the catalytic subunit of cyclic AMP-dependent protein kinase. This result is consistent with findings from studies indicating an influence of the kinase on the expression of protein-trafficking functions in <I>C. neoformans</I>.</P>